384 MR JOHN S. FLETT ON 



& 



graph on the Old Red Sandstone of Western Europe.* As the result of two visits to 

 Orkney, in which he was accompanied by Mr B. N. Peach, he pointed out that the yellow 

 sandstones of Hoy did not pass down conformably into the flagstones which form the 

 basis of that island, but were separated from them by a marked unconformity. At 

 the base of the upper sandstones lay a series of contemporaneous lavas and ash beds, 

 which were in all probability erupted from certain ' necks ' in the low-lying district at 

 the foot of the Hoy Hills. These rocks he regarded as belonging to the upper Old Red 

 Sandstone. The lower Old Red Sandstone consisted principally of a great thickness of 

 flagstones, with which were interstratified beds of yellow and red sandstone, and 

 occasionally of conglomerate. The fossils belonged exclusively to this lower series ; and 

 a table is given, compiled by Mr C. W. Peach, showing the distribution of fossil fishes 

 in the lower Old Red Sandstone of Lake Orcadie, including those of Orkney so far as 

 known at that time. As Sir Archibald Geikie anticipated, subsequent revision has 

 necessitated "considerable pruning of the fossil lists." The conglomerates around the 

 granite axis of Stromness formed merely a local base, " due to the uprise of an old ridge 

 of rock from the surface of the sheet of water in which these strata were accumulated," 

 and were presumably not on the same horizon as the thick conglomerates on which, in 

 Caithness, the lowest flagstones rest. The sandstones interbedded with the flagstones in 

 South Ronaldshay were regarded as in all probability the northward continuation of the 

 similar rocks at Gill's Bay, Huna, and John o' Groats, on the south side of the Pent- 

 land Firth. From a geological point of view, the brief notice of the Old Red Sandstone 

 of the Orkneys contained in this paper forms by far the most important contribution to 

 the knowledge of the subject published up to that time. 



In two papers on the Geognosy of Orkney,t published in December 1879, Professor 

 Foster Heddle showed the existence of a well-marked syncline beginning in the North 

 Isles in the island of Eday, and continuing thence through Shapinshay and Inganess Bay 

 to Scapa and the north-west corner of South Ronaldshay. The beds which occupy the 

 centre of this trough are coarse arenaceous freestones, which rest perfectly conformably 

 on the ordinary blue flags of the islands, and at Heclabir, in Sanday, contain thin beds 

 of conglomerate. These sandstones cannot, in consequence, be the same as the yellow 

 sandstones of Hoy, which unconformably overlie the flags. In these papers many 

 interesting details are given of the minerals occurring in the islands, and of the structural 

 peculiarities of the flagstones, especially as seen in the magnificent coast sections. 



In 1880 Messrs Peach and Horne made a much more detailed examination of the 

 islands than had previously been attempted, and the result was an important paper on 

 the Old Red Sandstone of Orkney. | They showed that in all probability the upper Old 

 Red Sandstone of the district was confined to the island of Hoy, while the rest of the 



* Sir Arch. Geikie, " The Old Red Sandstone of Western Europe, " pt. i., Trans. Roy. Soc. Edin., vol. xxviii. pp. 409 

 and 410. 



t Mineralogical Magazine, " The Geognosy and Mineralogy of Scotland," part v.— Orkney, M. Foster Heddlk, M.D., 

 1880, p. 102. 



X I'roc. Roy, Phys. Soc. Edin. 1880 



